On their journey from their source to Earth, electrically-charged cosmic rays are deflected by magnetic fields.
While small-scale magnetized structures have no impact on the propagation of ultra-high-energy cosmic rays, they can have an impact on our reconstruction of the large-scale magnetic field obtained from synchrotron and Faraday rotation data. In this context, the Local Bubble, a cavity of hot gas surrounded by a thick magnetized dusty shell, is perhaps one of the most important foregrounds to consider as it surrounds us.
In this work, we use a new analytical model to describe the divergence-free magnetic field in the shell of Galactic bubbles to assess the impact of the geometric characterization of the Local Bubble shell on predictions of its contribution to Galactic magnetic field observables.
We show that the choice of the shape of the Local Bubble shell and the location of the explosion that has led to the formation of the bubble are important factors to consider. They are decisive in estimating the contribution of the magnetized shell of the Local Bubble to synchrotron polarized emission and Faraday rotation measures.
In addition, we find that the contribution of the Local Bubble shell to synchrotron polarized emission is likely to be substantial at high Galactic latitudes. This may point to potential biases in current modeling of the large-scale Galactic magnetic field, and hence in back-propagation studies of ultra-high-energy cosmic rays. Further analysis will be required to fully ascertain the impact of this foreground.